Paleoceanographic changes on the Farallon Escarpment off central California during the last 16,000 years

Quaternary International
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Abstract

New benthic and planktic foraminiferal assemblage census data and Benthic Foraminiferal Oxygen Index (BFOI) values, previously published marine climate proxy data (stable isotopes and Ca/Cd), and unpublished results of total carbon, organic carbon, and calcium carbonate analyses of sediments recovered off central California on the Farallon Escarpment (1605m water depth; 37??13.4???N, 123??14.6???W; core F-8-90-G21) document paleoceanographic changes during the latest Quaternary which reflect the intensity and source of North Pacific Intermediate Water (NPIW) and surface productivity. Accelerator mass spectrometry radiocarbon dates of both benthic and planktic species provide an excellent age-depth model for the last 16,000 years, covering the latest glacial, B??lling-Aller??d, Younger Dryas, and early, middle, and late Holocene intervals. A Q-mode cluster analysis separated the benthic fauna into three clusters, one Pleistocene and two Holocene, whereas the planktic fauna was divided only into Pleistocene and Holocene clusters. Stable oxygen isotope values show an increase in water temperature of ~1??C from the late glacial to late Holocene and a change in faunal composition of the planktic assemblage implies surface waters warmed as well. A general trend of decreasing dissolved oxygen concentration from the Pleistocene (high oxic; 3.0-6.0+ ml/l O2) to the Holocene (low oxic; 1.5-3.0ml/l O2) suggested by the BFOI and Cd/Ca data reflect decreased ventilation as the source of the NPIW shifted from the Sea of Okhotsk to the tropical east Pacific at ~11,000 cal BP. The middle Holocene cooling reported in other central and northern California margin studies is not apparent in F-8-90-G21, which compares more favorably with studies from southern California and British Columbia. Total carbon and organic carbon values are highest in the B??lling-Aller??d, early Holocene, and late Holocene. Similarly, calcium carbonate values are high in the B??lling-Aller??d and peak in the early Holocene, but decrease significantly in the latest middle and late Holocene which coincides with a depauparate planktic foraminiferal fauna in the upper 60cm (~70000-0 cal BP) of the core and poor preservation of the benthic foraminiferal fauna at 40cm (~3000 cal BP). Decoupling is evident between the planktic and benthic faunal response to changing climatic conditions, with the surface-dwelling assemblage often leading the bottom-dwelling assemblage by several millennia. ?? 2010.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Paleoceanographic changes on the Farallon Escarpment off central California during the last 16,000 years
Series title Quaternary International
DOI 10.1016/j.quaint.2010.09.005
Volume 235
Issue 1-2
Year Published 2011
Language English
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Quaternary International
First page 26
Last page 39